A polyamide is one of the polymers which are frequently used as engineering plastics for a very wide range of applications.
A polyamide composition is of significant commercial interest and may be used to produce housings or housing parts in various applications, including motor vehicles, industrial machines, home electronic appliances, for example, a fuel filter housing for a diesel engine, generally by injection molding.
In 1994, the European Union (EU) adopted the ATEX Directive 94/9/EC, which establishes technical and legal requirements for products intended for use inside hazardous areas with potentially explosive atmospheres. ATEX derives its name from the French title of the 94/9/EC Directive, i.e., Appareils destinés àêtre utilisés en Atmosphères Explosibles. As of July 2003, it is mandatory to use products which have an ATEX type approval within EU. Any product placed on the market or put into use in hazardous environments regulated by the ATEX Directive is required to meet the standards stipulated therein. The standards vary depending on the classification of the hazardous areas.
One of the standards for equipments in hazardous areas requires that polymer housings containing electrical equipment be electrically conductive. The main concern of the Directive is a potential build-up of static charges within the polymer housing. If sufficient static charges are built up, then there exists a potential for spark, which in a gaseous or dusty environment presents a significant risk of explosion or fire.
In order to provide stability against fire or explosion due to such a build-up of static charges, which may occur during fuel filtering in diesel engines, electrical conductivity is required and thus attempts have been made to increase electrical conductivity of a polymer composition intended to be used to produce a fuel filter housing by incorporating electrically conductive materials such as carbon fibers or carbon black into the polymer composition.
However, a polymer composition comprising such conductive materials generally shows uneven distribution of electrical surface conductivity by injection molding according to injection pressure and speed, and the electrical surface conductivity changes according to the distance from gate in an injection mold. That is to say, the electrical surface conductivity decreases as such distance increases.
In order to obtain a uniform distribution of electrical conductivity, therefore, more conductive materials are to be added and therefore a problem of overdesign may occur.
Accordingly, a polymer composition, which can accomplish a rather uniform distribution of electrical conductivity with less addition of conductive materials while still exhibiting excellent electrical conductivity, is required in this technology field.